A dialysis machine of the known type generally comprises a blood circulation circuit, a dialysate circulation circuit and a filter, which is provided with a dialysate compartment, a blood compartment and a semi-permeable membrane to separate the dialysate compartment from the blood compartment. The dialysate compartment is connected to the dialysate circuit, while the blood compartment is connected to the blood circuit, in such a way that the blood to be treated and the dialysate, generally flowing in opposite directions, pass through the blood compartment and the dialysate compartment respectively during the dialysis treatment.
During the dialysis treatment, unwanted particles contained in the blood migrate from the blood compartment to the dialysate compartment through the semi-permeable membrane both by diffusion and by convection, as a result of the passage of some of the liquid contained in the blood towards the dialysate compartment. Thus the patient will have lost some weight by the end of the dialysis treatment.
In operation, the blood circuit is connected to the patient's cardiovascular system to collect the blood to be treated and return the treated blood to the patient, and comprises a venous branch and an arterial branch, which is partially wrapped around a lobed rotor to form a peristaltic blood circulation pump.
Before the dialysis treatment is started, the filter must be filled by an operation generally called “priming”, and the filter must then be washed in order to eliminate air bubbles, which may be formed in the initial stage of circulating a liquid through the filter, and preservatives which are used to sterilize the filter and the blood circuit. According to the known methods of filter washing, the blood circuit is made into a closed loop, a bag of physiological saline is connected to a branch of the blood circuit, and the physiological saline is recirculated in the blood circuit.